*2.2. Technological Algorithm of Solid Ceramic End Mill Manufacturing*

The technological algorithm for solid ceramic end mills manufacturing developed by the study's authors is visualized in Figure 3. It includes the following technological operation steps when the finishing operation of coating is not indicated on the diagram:


**Figure 3.** Technological algorithm for manufacturing solid ceramic end mills.

#### *2.3. Powder Compositions' Preparation and Sintering Ceramic Blanks*

Powders produced by Plasmotherm (Moscow, Russia) were used as initial ceramic precursors: α-SiAlON and β-SiAlON with a particle size of 1 ± 0.5 μm and TiN additives with a particle size of 15–175 nm. The colloidal method was used for mixing the ceramic powder composition since it allows mixing with minimal time and energy costs.

Three suspension options based on powder compositions were prepared in a ball mill for 24 h using isopropyl alcohol and ceramic grinding bodies in a polyethylene container. The choice of composition content was made taking into account the data of previous

works conducted by authoritative researchers and based on the professional experience of the current study authors [22,31,32]:


The resulting suspensions were dried using a vacuum drying oven, VO400, at +50 ◦C for 24 h (Memmert GmbH + Co. KG, Schwabach, Germany). After drying, the powders were sieved using a vibration machine (NL 1015X/010, NL Scientific, Klang, Malaysia), sieve laboratory control of 2 ± 0.5 μm, and Si3N4 ceramic grinding bodies [48].

After completing all the preparatory operations, the powder compositions were subjected to spark plasma sintering on a technological unit manufactured by FCT Systeme GmbH (Effelder-Rauenstein, Germany) (Figure 4).

**Figure 4.** A schematic diagram of the ceramic composition's spark plasma sintering.

Ten disk-shaped samples of 3.0 mm thickness and 20.0 mm diameter were made from each version of the powder composition. Further, they were subsequently used to assess sintered samples' main physical and mechanical properties. The ceramic composition that exhibits the best results was subsequently used for coating and tribological tests. The sintering pressure was constant for all types of materials and amounted to 80 MPa, and the holding time at the maximum temperature was 30 min. The sintering temperature was varied from 1600 to 1750 ◦C with a pitch of 50 ◦C. These indicators were selected based on the analysis of technical literature [28,30,32] and preliminary experiments carried out by the authors of the current work with spark plasma sintering ceramics based on SiAlON. During sintering, the pressure value was considered rational because its effect on the final samples' mechanical properties was described in a previously published study by the authors of [49]. After determining the powder composition's optimal version and choosing a rational sintering temperature mode, disk-shaped ceramic blanks with 10.2 mm thickness and 80.0 mm diameter were made, from which ceramic rods were obtained.
